'The horse has bolted' when it comes to teenagers use of e-cigarettes, according to the Irish Heart Foundation.
It comes as new laws will ban the sale of e-cigarettes to those under-18.
The legislation also bans the advertising of nicotine products near schools and on public transport, and reduces the number of vendors permitted to sell them.
Mark Murphy is Advocacy Manager with the Irish Heart Foundation.
He told Breakfast Briefing while the new law is welcome, it took too long to get here.
"The law is incredibly delayed and it's been a long time coming," he said.
"Unfortunately the horse has bolted when it comes to teenage youth use of e-cigarettes.
"We know from statistics that the use of e-cigarettes among children and teenagers has been increasing... and we know that e-cigarette use is a gateway to smoking".
Mr Murphy said evidence suggests younger people who use e-cigarettes are "up to five-times more likely to smoke."
"We've seen an increase in youth use of e-cigarettes and smoking for the first time in decades.
"This is just the start; we need far more regulations to come in, and deter young people from using e-cigarettes".
He said this should include a ban on flavours and disposable vapes.
"We know from research that young people who start e-cigarettes most likely use a flavoured vape.
"It entices people, it helps initiation - and there's over 10,000 types of different kind of flavours you can get," he added.